JP2005136540A - A/d conversion array and image sensor - Google Patents

A/d conversion array and image sensor Download PDF

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JP2005136540A
JP2005136540A JP2003368340A JP2003368340A JP2005136540A JP 2005136540 A JP2005136540 A JP 2005136540A JP 2003368340 A JP2003368340 A JP 2003368340A JP 2003368340 A JP2003368340 A JP 2003368340A JP 2005136540 A JP2005136540 A JP 2005136540A
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conversion
output
input
image sensor
capacitor
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JP3962788B2 (en
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Shoji Kawahito
祥二 川人
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National Univ Corp Shizuoka Univ
国立大学法人静岡大学
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    • HELECTRICITY
    • H03BASIC ELECTRONIC CIRCUITRY
    • H03MCODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M1/00Analogue/digital conversion; Digital/analogue conversion
    • H03M1/06Continuously compensating for, or preventing, undesired influence of physical parameters
    • H03M1/0617Continuously compensating for, or preventing, undesired influence of physical parameters characterised by the use of methods or means not specific to a particular type of detrimental influence
    • H03M1/0675Continuously compensating for, or preventing, undesired influence of physical parameters characterised by the use of methods or means not specific to a particular type of detrimental influence using redundancy
    • H03M1/069Continuously compensating for, or preventing, undesired influence of physical parameters characterised by the use of methods or means not specific to a particular type of detrimental influence using redundancy by range overlap between successive stages or steps
    • H03M1/0695Continuously compensating for, or preventing, undesired influence of physical parameters characterised by the use of methods or means not specific to a particular type of detrimental influence using redundancy by range overlap between successive stages or steps using less than the maximum number of output states per stage or step, e.g. 1.5 per stage or less than 1.5 bit per stage type
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04NPICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N5/00Details of television systems
    • H04N5/30Transforming light or analogous information into electric information
    • H04N5/335Transforming light or analogous information into electric information using solid-state image sensors [SSIS]
    • H04N5/357Noise processing, e.g. detecting, correcting, reducing or removing noise
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04NPICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N5/00Details of television systems
    • H04N5/30Transforming light or analogous information into electric information
    • H04N5/335Transforming light or analogous information into electric information using solid-state image sensors [SSIS]
    • H04N5/369SSIS architecture; Circuitry associated therewith
    • H04N5/378Readout circuits, e.g. correlated double sampling [CDS] circuits, output amplifiers or A/D converters
    • HELECTRICITY
    • H03BASIC ELECTRONIC CIRCUITRY
    • H03MCODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M1/00Analogue/digital conversion; Digital/analogue conversion
    • H03M1/12Analogue/digital converters
    • H03M1/34Analogue value compared with reference values
    • H03M1/38Analogue value compared with reference values sequentially only, e.g. successive approximation type
    • H03M1/40Analogue value compared with reference values sequentially only, e.g. successive approximation type recirculation type
    • H03M1/403Analogue value compared with reference values sequentially only, e.g. successive approximation type recirculation type using switched capacitors

Abstract

<P>PROBLEM TO BE SOLVED: To provide an A/D conversion array for an image sensor whose area and power consumption are reduced by reducing the number of amplifiers and capacitors (capacity) compared to that of a conventional cyclic type A/D conversion array and further providing a function of canceling noise generated at a pixel part of an image sensor. <P>SOLUTION: After an input signal Vin is applied to a C1 and held, a reset level is applied to the Vin and a difference signal is amplified at a radio (C1/C2) of the C1 and a C2 connected to an inverting amplifier. Then the output of the inverting amplifier is held and the output of the inverting amplifier is converted by a comparator from analog to digital; and a control signal is generated from the conversion output to turn on one of switches which are controlled with ϕM1, ϕO1, and ϕP1. A digital signal is converted into an analog signal, which is subtracted from the signal held in the C1. This signal is amplified, converted again from analog to digital, and the same operation is cyclically repeated. Consequently, noise cancellation and multi-bit A/D conversion are achieved. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a technique for integrating an A / D converter in a column of an image sensor, in particular, a CMOS image sensor to obtain a digital output and to enable high-speed signal reading. This technique is useful as an image sensor having a function of concentrating signals from an image sensor and reading them out in a short time, or an image sensor for high-speed imaging.

As described above, conventional techniques for performing A / D conversion in a column of a CMOS image sensor include the following.
[1] Japanese Patent No. 2532374
[2] A. Simoni, A. Sartori, M. Gottaidi, A. Zorat, “A digital vision sensor,” Sensors and Actuators, A46-47, pp. 439-443, 1995.
[3] T. Sugiki, S. Ohsawa, H. Miura, M. Sasaki, N. Nakamura, I. Inoue, M. Hoshino, Y. Tomizawa, T. Arakawa, "A 60mW 10b CMOS image sensor with column-to -column FPN reduction, "Dig. Tech. Papers, Int. Solid-State Circuits Conf.," pp.108-109,2000.
[4] B. Mansoorian, HY Yee, S. Huang, E. Fossum, "A 250mW 60frames / s 1280x 720 pixel 9b CMOS digital image sensor," Dig. Tech. Papers, Int. Solid-State Circuits Conf., " pp.312-313,1999.
[5] S. Decker, RD McGrath, K. Bremer, CG Sodini, “A 256 x 256 CMOS imaging array with wide dynamic range pixels and column-parallel digital output,“ IEEE J. Solid-State Circuits, vol. 33, no. 12, Dec. 1998.

The above [1] integrates an 8-bit integrating A / D converter element using a ramp signal generator, a comparator, and a register in a column. A similar one is reported in [2]. Similarly, [3] is an integration type A / D converter element integrated in a column, and 10b is realized by using a comparator with improved accuracy. These integration type A / D converters have a long conversion time, and especially when the resolution is increased, the conversion time becomes exponentially longer. Therefore, it is difficult to realize a higher resolution as it is. However, there is an advantage of excellent linearity.
Further, [4] is an operation in which successive approximation A / D converters using capacitors are arranged in a column and can be operated at a high speed, so that an image sensor having a high frame rate and a large number of pixels is possible. Suitable for However, this is also only about 8 bits in actual accuracy. [5] is one in which two-stage cyclic A / D converter elements are arranged in a column for operation, and this is also suitable for high-speed A / D conversion. However, since two amplifiers are used, the circuit scale increases.

In addition to these, some image sensors having A / D conversion elements in the pixel have been reported, but they are omitted because they are not directly related to the present invention.
Japanese Patent No. 2532374 A. Simoni, A. Sartori, M. Gottaidi, A. Zorat, "A digital vision sensor," Sensors and Actuators, A46-47, pp. 439-443, 1995. T. Sugiki, S. Ohsawa, H. Miura, M. Sasaki, N. Nakamura, I. Inoue, M. Hoshino, Y. Tomizawa, T. Arakawa, "A 60mW 10b CMOS image sensor with column-to-column FPN reduction, "Dig. Tech. Papers, Int. Solid-State Circuits Conf.," pp.108-109,2000. B. Mansoorian, HY Yee, S. Huang, E. Fossum, "A 250mW 60frames / s 1280x 720 pixel 9b CMOS digital image sensor," Dig. Tech. Papers, Int. Solid-State Circuits Conf., "Pp.312 -313,1999. S. Decker, RD McGrath, K. Bremer, CG Sodini, "A 256 x 256 CMOS imaging array with wide dynamic range pixels and column-parallel digital output," IEEE J. Solid-State Circuits, vol. 33, no. 12 , Dec. 1998.

  Prior art [5] is most relevant to the present invention and will be described with reference to the circuit. As shown in FIG. 1, a circuit that performs 1-bit A / D conversion is connected in two stages, and its output is returned to the input to perform cyclic A / D conversion. In such a system, an amplifier is required for each stage, which increases the area and power consumption. Further, when used as an A / D converter integrated in the column of the image sensor, three amplifiers are required for each column, including a noise canceling amplifier and an A / D converter amplifier.

FIG. 2 shows the configuration of the CMOS image sensor of the present invention in which an A / D converter is integrated in a column. The signal read to the column reading circuit in units of rows is first subjected to noise cancellation, and the signal is given to the cyclic A / D conversion circuit for each pixel. Here, A / D conversion with a necessary resolution is performed, and the digital value is read out by horizontal scanning. In order to read out a signal at a high speed, the horizontal scanning is not carried out in series, but a partial horizontal scanning is performed in parallel by providing a plurality of outputs, as shown in FIG. There are many ways to multiplex outputs and output digitized signals in parallel on multiple lines. As will be described later, in FIGS. 2 and 3, one part, that is, noise cancellation and cyclic ADC can be configured and integrated using one amplifier.
As will be described below, as a cyclic A / D conversion, a redundant expression that takes three values of -1, 0, 1 in binary, for example, is used per cycle. Ultimately, in order to reduce the number of data output lines In addition, after being converted into a non-redundant representation, the digital data is subjected to horizontal scanning (or partial horizontal scanning for parallel output) and output. When the output data rate is low, the redundant representation may be converted to the non-redundant representation after horizontal scanning. In the case of N bits, this conversion can be performed using an adder that performs addition of N + 1 digits.

The present invention is characterized in that the number of amplifiers and the number of capacitors for performing cyclic A / D conversion are reduced. FIG. 4 shows a circuit example of the cyclic A / D converter of the present invention that performs A / D conversion of 1 bit or 1 bit and a half per cycle. This is equivalent in function to FIG.
FIG. 5 shows conversion characteristics of the cyclic A / D converter of FIG. In FIG. 4, V RM and V RP correspond to Vref and −Vref in FIG. The relationship between the digital outputs D0, D1 in FIG. 4 and D in FIG. 5 and the input signal Vin to the comparator (3) is as follows.
That is, the input is divided into three areas: (1) -Vref to -Vref / 4, (2) -Vref / 4 to Vref / 4, and (3) Vref / 4 to Vref. A / D conversion is performed and digital codes of -1, 0, 1 are assigned. The first code is the most significant digit. Calculation is performed according to the characteristics of FIG. 4 to generate an output. The calculation is expressed by the following equation.
In other words, A / D conversion is performed in order from the upper digit, the input is doubled, and a constant value is drawn by the A / D conversion value, so that the output is always in the range of ± Vref. By applying this again to the input and repeating the same, multi-bit A / D conversion is performed. At this time, since A / D conversion is performed with three values per time (one digit), redundancy occurs in the digital value. This redundancy greatly reduces the accuracy requirement of the comparator and enables highly accurate A / D conversion.

  In binary numbers, binary values of 0 and 1 are taken for each digit, but ternary values of -1, 0, and 1 are taken for each digit, so 1.5-bit A / D conversion is performed per stage. Can be considered. As an actual operation, as shown in FIG. 6, at first, a switch by a control signal φA (hereinafter abbreviated as φA) is turned on, an input signal is given, and a calculation of 1.5 bits per stage is performed. Based on the result, an operation is performed according to equation (2). The output is stored in an S / H (sample hold) circuit. This completes the first cycle. Next, the switch by the control signal φB (hereinafter abbreviated as φB) is turned on, the switch by φA is turned off, and the output of the S / H circuit is given to the A / D converter of the 1.5-bit bit. Repeat that. If this is repeated N times, N + 1 bit A / D conversion can be performed.

4 reduces the number of necessary amplifiers and capacitors while realizing the same function as FIG. The operation timing chart is shown in FIG. FIG. 7 shows up to the third cycle.
In FIG. 4, first, Vin is sampled to both C1 and C2, and then C2 is connected between the input and output of the inverting amplifier (2), and 1.5 bits according to equation (1) are obtained by two comparators. A / D conversion is performed. C1 is connected to the D / A converter. Thereby, the calculation of the following equation is executed.

If C1 = C2, this is equivalent to equation (2). Here, Vout (0) is the output of the first cycle, and D (0) is the first A / D conversion value, that is, the value of the most significant digit. In order to sample and hold the output, an S / H circuit is provided in FIG. 6, but in FIG. 4, the capacitance and the switch are controlled so as to perform an equivalent process. First, Vout (0) is originally stored in C2. Therefore, the voltage between Vout (0) and the ground point is stored using C1, and then this is converted into the virtual of DAC (digital / analog converter) and inverting amplifier (2) according to the result of A / D conversion. If reconnected between ground points, the charge is proportional to the difference.
Is transferred to C2, and as a result, the following equation is executed.

This is repeated as many times as necessary.
By taking the configuration of FIG. 4, an A / D converter is configured using one inverting amplifier (2) and two capacitors. Since this has a simple circuit configuration, it is possible to perform a high-speed A / D conversion as a whole by arranging a plurality of them and operating them by applying input signals in parallel.

  Here, the basic operation of the circuit will be described. First, the capacitors C1 and C2 are both connected to the input (Vin) and charged with the voltage Vin. If the respective charges are Q1 and Q2, then Q1 = C1 · Vin and Q2 = C2 · Vin. Thereafter, one end of the capacitor C2 is connected to the output terminal of the inverting amplifier (2). That is, the charge of Q2 is charged from the beginning to the capacitor C2. One end of the capacitor C1 is switched to a DAC (digital / analog converter). Assuming that the DAC output voltage is Vdac, the terminal voltage of the capacitor C1 changes from Vin to Vdac. Therefore, the change in the charge charged in the capacitor C1 is ΔQ1 = C1 (Vin−Vdac). Forwarded to C2. As a result, the final output is Vout = (Q2 + ΔQ1) / C2 = ((C1 + C2) Vin−C1 · Vdac) / C2. If C1 = C2 is selected, Vout = 2Vin-Vdac, so that the basic operation of the cyclic A / D conversion can be performed by doubling the input and subtracting the DAC output. The conventional cyclic type has an S / H circuit at the output of the amplifier. In order to sample and cycle the output of the S / H circuit, the above basic operation is repeated.

  In the circuit proposed by the inventor, since this operation is performed by one amplifier, the voltage Vin described above becomes the output voltage Vout of the amplifier at the time of circulation. Therefore, Vin of the above-mentioned “charging C2 with Vin” is This corresponds to Vout during the patrol. That is, since C2 is charged with Vin (= Vout) from the beginning, only C1 is connected to Vout (= Vin) first, and then the connection is switched to the DAC, Vout = 2Vin−Vdac. Can be calculated. In this case, C1 = C2 is selected. Thereby, a capacitor can be reduced from the conventional type.

  In order to make the noise cancel operation and the cyclic A / D conversion operation described later compatible, C1 is connected between the input Vin and the input of the inverting amplifier, and C2 is connected between the input and output of the inverting amplifier. The charge of C2 is initialized (Q2 = 0), and noise cancellation is performed by changing one end of C1 from Vs (signal voltage) to VR (reset voltage). As a result, when C1 = C2 is selected, Vout = ΔQ1 / C2 = C1 (Vs−VR) / C2 = Vs−VR and the gain is 1, but the noise canceling operation is performed by subtracting VR from Vs. It becomes. Thereafter, the cyclic A / D conversion operation is started.

FIG. 8 shows an example of a circuit in which 1.5-bit A / D conversion can be performed in half a clock by adding capacitors and using them alternately. The operation timing chart is shown in FIG. Although FIG. 8 shows up to the second cycle, in this way, 1.5-bit A / D conversion for four digits is executed in two cycles.
Here, two sets of comparators (3) are used for A / D conversion, but switching means are provided at the input and output of one set of comparators, and only one set is compared by using time division. It can also be configured with a vessel.

  Such a cyclic A / D converter arranged in an array is useful for performing A / D conversion by applying signals in parallel to an image sensor column. In this case, as shown in FIGS. 2 and 3, noise cancellation circuits for reducing noise generated in the pixel portion in the column are arranged in the column, and the above-described A / D converter arrays are arranged and operated on the output. However, as a more efficient circuit configuration, a noise canceling circuit or a circuit that performs amplification with a constant gain while canceling noise and a cyclic A / D conversion are integrated into one amplifier. It is possible to configure a circuit that performs noise cancellation / amplification and A / D conversion.

In the circuit shown in FIG. 10, a signal voltage (this is referred to as VS) by an optical signal is applied to Vin. This voltage is sampled to C1. At this time, the other of C1 is connected to the input of the inverting amplifier (2) in which φA and φ2 are turned on, and is substantially at the ground potential. Next, after φA is turned off, the photodiode portion is reset, and the reset voltage VR is applied to Vin. As a result, the electric charge resulting from the product of the voltage difference VR-VS and C1 is transferred to C2, and the voltage of the amplifier output changes. If the output voltage is Vout (0), this is expressed by the following equation.
That is, the difference between the signal level of the pixel portion and the reset level is amplified by a capacitance ratio of C1 / C2, and the fixed pattern noise of the pixel portion can be canceled. The output of the amplifier is subjected to 1.5-bit A / D conversion by two comparators (3), and the result is used to perform an operation for A / D conversion of the next digit. Subsequent operations are the same as those in FIG.

In the circuit of FIG. 10, the amplification degree is determined by the capacitance ratio of C1 / C2. When C1 is used for both noise cancellation and A / D conversion, it is necessary to set C1 = C2, and the ratio is 1. Therefore, a circuit is proposed in which the amplification factor is increased by adding a third capacitor C3 to the input. An example of the circuit is shown in FIG. The operation timing chart is shown in FIG.
In FIG. 11, C3 is a capacity used for amplification, and when amplification is not performed (that is, noise cancellation is performed with a gain of 1), the portion A of the broken line in FIG. 11 is deleted.
By setting C3 = (n-1) C0 and C1 = C2 = C0, the noise-cancelled signal can be amplified with a gain of n times. The pixel output of an amplification type image sensor using several transistors in the pixel shown in FIG. 13 is connected to Vin in FIG. Here, a case where three transistors are used (FIG. 13) will be described as an example. However, the present invention is not limited to this, and other amplification type images such as four transistors and five transistors that transfer charges in a pixel are described. It can also be applied to sensors.

In the case of a three-transistor amplification type image sensor, a voltage level generated as a result of accumulation of a signal in a photodiode (hereinafter referred to as Vs) is output to a selected pixel, and C1 and C3 in FIG. To sample. At this time, the switch by φA is turned on, the input / output of the inverting amplifier (2) is short-circuited, and the other of C1 and C3 is connected to the input of the inverting amplifier (2) at that time. Next, the switch by φA is opened, the voltage accumulated in the photodiode portion is reset (the switch by R is turned on), and the reset voltage level of the photodiode portion at this time (this is referred to as VR) is Vin in FIG. give. As a result, the electric charge resulting from the product of the voltage difference of VR−VS and C1 + C3 is transferred to C2, and the voltage of the amplifier output changes. If the output voltage is Vout (0), this is expressed by the following equation.
That is, the difference between the signal level of the pixel portion and the reset level is amplified by n times, so that the fixed pattern noise of the pixel portion can be canceled and the signal amplification can be performed. The output of the amplifier is subjected to 1.5-bit A / D conversion by two comparators (3), and the result is used to perform an operation for A / D conversion of the next digit. The subsequent operations are the same as those in FIG. 4, and C3 is used only during the first amplification, and is not used in the subsequent A / D conversion.

FIG. 11 shows an example of a circuit using an amplifier with one end grounded, but this can also be configured as a fully differential circuit. FIG. 14 shows an example of a circuit that performs the same processing as in FIG. 11 using a fully differential circuit. Also in FIG. 14, when amplification is not performed, the portion A is deleted.
Since FIG. 14 is fully differential, it is assumed that the input signal is given as a differential voltage between VIP and VIM. When the amplification type image sensor outputs a difference voltage between two signal lines in the pixel portion, the two inputs in FIG. 14 may be connected to the vertical signal line from the pixel portion. When the signal from the pixel unit is a single-ended signal and there is only one signal line, the VIP in FIG. 14 is connected to the vertical signal line from the pixel unit. For VIM in FIG. It is given as a voltage.

Next, FIG. 15 shows a circuit configuration when a noise canceling operation is performed using the method of FIG. 8 that performs A / D conversion of 1.5b in a half cycle for the column of the image sensor. The operation timing chart is shown in FIG. The operation is almost the same as in the case of FIG. 11, except that two sets of comparators (3) are used alternately every half cycle, and two capacitors C1 per half cycle are expressed by equation (4). Used for corresponding operations and output sample and hold operations.
Here, two sets of comparators (3) are used for A / D conversion, but switching means are provided at the input and output of one set of comparators, and only one set is compared by using time division. It can also be configured with a vessel.
Although the configuration of the fully differential circuit with respect to the circuit of FIG. 11 is shown, it is naturally possible to make the fully differential circuit also in FIGS. 4, 8, and 15. 4, FIG. 8, FIG. 11 and FIG. 14 can be easily inferred.

  With the above circuit, the capacity and the number of amplifiers can be reduced, but on the other hand, since there is no function to cancel the offset voltage of the amplifier, such an amplifier offset voltage and offset voltage due to switch injection are removed. It is necessary to. This can be eliminated by subtracting the offset voltage measured in advance in the digital domain for each column. However, there are cases where such processing cannot be easily performed. In such a case, it is necessary to make the circuit less susceptible to variations in the offset voltage of the amplifier. In that case, another amplifier is required, but the efficiency can be improved by also using the noise canceling amplifier of the image sensor.

An example of the circuit is shown in FIG. The operation timing chart is shown in FIG. When performing a sample of the signal level of the image sensor output, the switch controlled by .phi.A, first connect, be tied to the reference voltage V R, during amplification, the switch controlled by .phi.2d, between the amplifier input and output To do. Thereby, the offset voltage of the amplifier at the time of noise cancellation and amplification is canceled. Further, cyclic A / D conversion is performed in which the same amplifier is used to perform 1.5-bit A / D conversion per cycle. The output of the amplifier is stored by a sample and hold circuit. The sample hold circuit stores in the capacitor C4 with reference to the voltage shorted by the switch controlled by φ2A between the input and output of the amplifier A2, then opens the switch controlled by φ2 and φ2A, and controls C4 by φ1d The connected switch operates between the input and output of the amplifier. As a result, the sample hold circuit is not affected by the offset voltage of the amplifier.

  For the A / D conversion of the next digit, the output of the sample and hold circuit is sampled into C1 and C2 of the preceding circuit. At this time, the switch controlled by φ1A is sampled on the basis of the voltage shorted between the input and output of the amplifier A1, and then C2 is connected between the input and output of the amplifier by the switch controlled by φ2A. By connecting one terminal to the output of the DAC, the same calculation as in equation (3) is performed, but this operation is not affected by the offset voltage of the amplifier A1. In this manner, both the noise cancellation and the A / D conversion can be performed without receiving the amplifier offset voltage.

In the above, the case where two comparators are used and 1.5-bit A / D conversion is repeated per cycle has been described. However, a method of repeating one-bit A / D conversion using one comparator, It is possible to use a plurality of comparators and further amplify the amplifier by 4 times, 8 times, or 16 times, and cycle A / D conversion of multiple bits per cycle, and these methods are not excluded. .
Further, as shown in FIG. 19, a circuit for correcting an error caused by characteristic variations of a cyclic ADC or a noise cancellation circuit can be integrated in a column.
In addition, here, an inverting amplifier having a differential input is used as the inverting amplifier (2), but a similar circuit can be configured even if an inverting amplifier having no differential input and having a single-ended input is used. Is self-explanatory and does not preclude the adoption of these other amplifiers.

  The present invention realizes a high-speed and high-resolution image sensor by using a method for performing high-speed and high-resolution A / D conversion by arranging cyclic A / D converters in an array in an image sensor column. Provide a method. In particular, the number of amplifiers and capacitors (capacitance) is reduced compared to the conventional cyclic type, and the noise of the pixel part of the image sensor (reset noise, fixed pattern noise) is canceled. Perform cyclic A / D conversion using an amplifier. Thereby, an area and power consumption can be reduced.

Two-stage cyclic A / D converter (prior art) Configuration of image sensor with cyclic A / D converter integrated in column Configuration of an image sensor with a cyclic A / D converter integrated in a column (parallel output) Circuit configuration example of cyclic A / D converter that performs A / D conversion of 1.5 bits per time Conversion characteristics of a cyclic A / D converter that performs 1.5-bit A / D conversion per cycle Equivalent block diagram of a cyclic A / D converter that performs 1.5-bit A / D conversion per cycle Operation timing diagram of the A / D converter of FIG. Cyclic A / D converter that performs 1.5-bit A / D conversion in a half cycle Operation timing of the circuit of FIG. A / D converter for image sensor with integrated noise cancellation and A / D conversion A / D converter for image sensor with integrated noise cancellation / amplification and A / D conversion Operation timing chart of the circuit of FIG. 3-transistor pixel circuit Circuit example in which the circuit of FIG. 11 has a fully differential circuit configuration. A configuration that integrates a circuit that performs A / D conversion in half a cycle and a noise cancellation / amplification function Operation timing diagram of the circuit of FIG. A / D converter for image sensor with S / H amplifier Operation timing diagram of the circuit of FIG. Configuration for ADC error correction in the image sensor column

Explanation of symbols

1 Aggregation of noise cancellation circuit and cyclic AD converter 2 Inverting amplifier 3 Comparator
4 differential amplifier A1, A2 amplifier Ain, Vin signal input b, D binary value output Vref, Vr AD (analog / digital) conversion reference voltage Vrm, Vrp DA (digital / analog) conversion reference voltage C capacitance φ control Switch S / H controlled on / off by signal φ Sample hold circuit DAC DA (digital / analog) converter

Claims (7)

  1.   In the A / D conversion array, a circuit element for performing A / D conversion of N bits per cycle, a circuit element for D / A converting the digital output of the circuit element by the first switching means and the first capacitor, An amplifying means comprising a second capacitor connected between the input and output of the inverting amplifier for subtracting and amplifying the analog value of the conversion result from the analog input; A circuit element for sampling and holding the output of the amplifying means by the second switching means and the first capacitor, and selecting one of the output and the input signal of the amplifying means and selecting the selected signal as the first signal Unit circuits each including third switching means to be provided as an input to the amplifying means via a capacitor are arranged in an array, and the first circuit The control means of the third switching means is provided outside the array, the input signal is given as the input of the amplification means in the first stage, and the signal that has passed through the sample and hold circuit element is input to the amplification means in the next stage. To perform a cyclic multi-bit A / D conversion.
  2.   Two first capacitors used for D / A conversion in the amplifying means are provided, and the conversion speed per cycle is doubled by using these capacitors alternately for D / A conversion and sample hold. The A / D conversion array according to claim 1, wherein
  3.   2. The circuit element for performing N-bit A / D conversion divides an input analog signal into three regions according to voltage levels and assigns values of 1, 0, −1 to the three regions. A / D conversion array of description.
  4.   2. The A / D conversion array according to claim 1, wherein the amplifier in the amplifying means is constituted by a differential amplifier having a differential input and a differential output, and has a fully differential circuit configuration including its peripheral capacitors and switching means.
  5.   An A / D conversion array according to claim 1 is arranged in a column of an image sensor array, and A / D conversion is performed in parallel with respect to an output of the image sensor array.
  6.   A noise cancellation circuit is provided in the column of the image sensor array, and the noise cancellation circuit is connected to a second inverting amplifier and a third inverting amplifier connected between the output of the image sensor array and the input of the second inverting amplifier. A capacitor, a fourth capacitor connected between the input and output of the second inverting amplifier, and switching means for switching the connection, and the inverting amplifier in the cyclic A / D conversion array 6. The noise canceling circuit is also used as a second inverting amplifier, the first capacitor is also used as the third capacitor, and the second capacitor is also used as the fourth capacitor. Image sensor.
  7. Only during the noise canceling operation, a fifth capacitor is provided as a capacitor connected between the output of the image sensor array and the input of the inverting amplifier, and an amplification function is obtained by a capacitance ratio with the second capacitor. The image sensor according to claim 6.
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